This invention relates to machines for packaging rolls or groups of rolls in a film, and in particular to an adjustable girth control for a tube former in such machines.
In modern packaging machinery, rolled products, such as rolls of toilet tissue or paper towels, are conveyed individually or in groups, encapsulated in a plastic film formed into a tube, and the tube is then severed between succeeding products and sealed into individual packages. A basic packaging machine is illustrated and described in U.S. Pat. No. 4,430,844, which is assigned to the same assignee as the present application, and the disclosure of which is incorporated herein by reference.
In such machines, a girth former is included for forming plastic film into a tube extending about the products to be wrapped. The girth former is sized specifically to take into account the diameter and softness of the product being wrapped. Depending on softness or hardness of the product, diameter variations can occur, but those variations are limited by the sizing of the girth former. Therefore, diameter variations can cause serious production problems, particularly with harder-wrapped rolls which cannot compress sufficiently. The result is that such rolls may be too loosely wrapped with the plastic film, or the rolls may actually jam in the girth former, causing the machine to be shut down while the jam is cleared.
In the typical packaging machine such as depicted in incorporated U.S. Pat. No. 4,430,844, product is introduced into the area of the girth former and is conveyed into place, often being somewhat compressed by an upstream preformer section before entering the girth former. Often, the compression set in the preformer compresses the rolls somewhat more than necessary to enter the girth former to insure that the rolls properly enter the former without interference or jamming. As the rolls enter the girth former, they are encapsulated in a tube of film, and are also contacted by pull belts which move in unison with the product and the tube, ensuring a smooth transfer for downstream sealing.
Whenever a different product is to be packaged by the machine, the girth former must be changed. That change also requires adjustment of the preformer and realignment of the pull belts to ensure that product travels smoothly through the girth forming area.
The amount of film wrapped about the product traveling through the machine is dictated by the internal dimension of the girth former, and not by the size of the product itself. Therefore, if the product is smaller in diameter than intended, a loose wrap will result, which is undesirable. To overcome this problem, and to accommodate varying diameters of product traveling through the machine, an adjustable girth former is needed.